Beginning with the introduction of poly-(2-hydroxyethyl methacrylate) (poly-HEMA) by Wichterle (U.S. Pat. No. 3,220,960), hydrogels, that is water-insoluble, but water-swollen polymers have become ever more important as components in biomedical application, be they implants, prostheses or drug delivery devices, due to their excellent biocompatibility and permeability. Poly-HEMA based hydrogels have become the major soft contact lens material due to their outstanding comfort characteristics and sufficiently high oxygen permeability (O.sub.2.DK). Soft contact lenses conform very tightly to the cornea and therefore, at .about.0.1 mm thickness, need to have an O.sub.2.DK of at least 5-6 barrers, if damage to the cornea is to be prevented during daily wear.
The O.sub.2.DK of an acrylic polymer, which does not contain either silicone or fluorine, is primarily determined by its water content and rises from zero at zero % H.sub.2 O to 6.5 at .about.39% H.sub.2 O (for poly-HEMA), 12.5 at .about.50% H.sub.2 O to at 23.about.60% H.sub.2 O. However, as the water content is increased, hydrogel strength is drastically decreased and in order to maintain durability lens thickness has to be increased. This in turn counteracts the higher O.sub.2.DK, because it reduces oxygen-transmissibility, P=O.sub.2 DK/l (l=lens thickness).
It is highly desirable to have a contact lens material, or indeed a hydrogel for biomedical applications in general, which is strong, comfortable to wear and has an inherently much higher O.sub.2.DK than conventional hydrogels. Such hydrogels can be made by incorporation of other oxygen-flux enhancing groups into the polymer, most notably siloxane groups and fluoroalkyl groups.
Both types of hydrogels have been described in the prior art. Polysiloxane-dimethacrylate as well as polysiloxane-block-polyethyleneoxide dimethacrylate copolymers with water soluble vinyl monomers have been described in U.S. Pat. No. 4,136,250 for use in drug delivery, but also for contact lens applications; similar compositions are disclosed in U.S. Pat. No. 4,605,712.
Although these polymers show excellent strength and toughness, they are limited in the amount of siloxane groups which can be incorporated without producing phase-separation and opacity because the siloxane is part of a rather high molecular weight polysiloxane block.
Larger amounts of siloxane groups can be built into clear hydrogels, if oligosiloxanyl-silyl alkyl (meth)-acrylates are used as comonomers; a more random distribution of siloxane groups prevents the formation of large, incompatible domains.
Such oligosiloxanyl-silyl groups containing hydrogels of prior art, which are useful as contact lens materials are disclosed in U.S. Pat. No. 4,139,692 and U.S. Pat. No. 4,139,513, specifying tri-siloxy alkylmethacrylate, with the OH-group required for compatibility.
U.S. Pat. No. 4,182,822 and U.S. Pat. No. 4,343,927 describe N-vinyl pyrrolidone and C.sub.1 -C.sub.4 -dialkyl acrylamide-copolymers with oligosiloxanyl alkylenemethacrylates.
The following patents describe prior art compositions consisting of fluorinated hydrogels. U.S. Pat. No. 4,433,111, and U.S. Pat. No. 4,493,910 describes hydrogels and contact lenses obtained by copolymerization of 20-40 mol % substituted or unsubstituted acrylamide or methacrylamide; 25-55 mol % N-vinylpyrrolidone (NVP); 5-10% mol hydroxy-alkyl(meth)-acrylate; 1-10 mol % (meth)-acrylic acid, and 1-9 mol % of a perfluoroalkyl-alkylene (meth)acrylate; the perfluoroalkyl groups act to reduce protein deposition.
U.S. Pat. No. 4,640,965, describes hydrogels and contact lenses obtained by copolymerization of hydroxyfluoroalkyl styrene (5-60%, by weight) with hydroxyalkyl (meth)-acrylates or N-vinylpyrrolidone (40-95%, by weight); the hydroxy group is necessary to attain the required compatibility.
U.S. Pat. No. 4,638,040 describes the synthesis of 1,3-bis(trifluoroacetoxy) propyl-2-methacrylate polymers and their use as hydrogel-contact lens materials and ocular implants after hydrolysis.
U.S. Pat. No. 4,650,843 describes hydrogel contact lens materials consisting essentially of copolymers of 59-95% (by weight) of 2-hydroxyethyl methacrylate and 5-35% (by weight) of fluorinated methacrylates with up to 5 F-atoms.
In most cases the range of clear compositions is very limited; the commercially available fluorinated (meth)acrylates can be incorporated in only relatively small amounts; alternatively, complicated, hydroxylated F-monomers have to specially be synthesized to achieve better solubility in NVP or HEMA (U.S. Pat. No. 4,640,965).
In copending patent application Ser. No. 356,801 now U.S. Pat. No. 4,954,587 we have described unique, highly oxygen permeable fluorinated hydrogels which are copolymers of perfluoroalkyl substituted (meth)-acrylates and N,N-dimethyl-acrylamide.
In all the prior art examples, low molecular weight monomers serve as starting materials for the polymerization. While this is convenient for doing bulk-polymerizations in a closed mold, it is less practical for curing of films or surface coatings, for example by UV-irradiation; then large amounts of monomers can evaporate, posing health hazards and irreproducibly altering the composition of the coating. Also, because of the high concentration of reactive double bonds during bulk polymerization, and the exothermic nature of the reaction, temperature is often difficult to control and shrinkage can occur in the mold as well. On the other hand, if solution polymerizations are carried out, as is sometimes desirable when otherwise incompatible comonomers have to be combined, long polymerization times are required to achieve high conversions of monomers.
It has now been discovered that linear, water soluble copolymers with a high siloxane and/or fluorine content and pendent vinyl unsaturated groups can be prepared in high yield, which are ideally suited to make by UV-curing water swellable and oxygen permeable coatings and films or shaped articles, like contact lenses. These linear unsaturated copolymers, hereinafter called prepolymers, are made in a two-step process by:
(1) copolymerization, in bulk or in solution of A) oligosiloxanylsilyl-alkyl methacrylates or perfluoroalkyl substituted alkyl acrylates or methacrylates as oxygen flux enhancing comonomers; (B) a comonomer mixture consisting of a N,N-dimethylacrylamide or N-vinylpyrrolidone as main hydrophilic comonomers; (C) active hydrogen containing vinyl comonomers, such as primary or secondary-amino alkyl- or hydroxy alkyl vinyl compounds; (D) optionally other copolymerizable ethylenically unsaturated monomers; and (E) also optionally, a chain transfer agent; followed by:
(2) reaction with a isocyanato substituted ethylenically unsaturated monomer (M.sub.v), 0.1 to 10 mol %, based on C.sub.2 -mer units of the prepolymer chain.
Vinyl unsaturated prepolymers, obtained by reaction of an active hydrogen containing prepolymer with a vinyl unsaturated isocyanate, which do however not contain silicone or fluorine, have been described in the literature; for example in U.S. Pat. No. 3,928,299, which discloses very broadly an unsaturated polymer of over 1000 MW; neither silicone, fluorine or hydrogels are mentioned or disclosed; in U.S. Pat. No. 4,548,983, which describes hydrogels based on alkylene glycol mono-(meth)acrylates, not N,N-dimethylacrylamide or N-vinylpyrrolidone, and which are made as shaped hydrogel articles by solution polymerization in a mold, also without fluorine or silicone.
U.S. Pat. No. 4,383,091 discloses the reaction product of a poly-hydroxy substituted polyglycidyl ether with 2-isocyanatoethyl methacrylate.
Vinyl unsaturated prepolymers obtained by reaction of a 2-isocyanatoethyl methacrylate copolymer with, for example, 2-hydroxyethyl methacrylate, are described in U.S. Pat. No. 4,343,919.
No unsaturated, linear, water soluble or, after a final crosslinking step, highly water swellable copolymers have been described, which are at the same time high in fluorine or silicone content.
It is an object of this invention to provide an easily polymerizable fluorine and/or silicone containing hydrophilic prepolymer; it is a further object of this invention to provide a highly water swellable, fluorine and/or silicone containing crosslinked polymer with high oxygen permeability, which is obtained by free radical polymerization of the hydrophilic prepolymer either by itself or in combination with up to 50% by weight of other copolymerizable vinyl monomers, M-2.